The present invention relates to a wavelength multiplexing/de multiplexing unit, a wavelength multiplexing/de multiplexing apparatus and a wavelength multiplexing/de multiplexing method which are available for optical communications or the like.
Wavelength division multiplexing (WDM) is a technique of combining a plurality of optical waves of different wavelengths for transmission over a single optical fiber and used to expand the transmission capacity of trunk lines of the Internet or the like.
A wavelength multiplexing/demultiplexing circuit plays a key role in WDM. That is, the wavelength multiplexing/demultiplexing circuit is a device arranged to combine a plurality of optical waves of different wavelengths at the transmitting end and a separating wavelength multiplexed optical wave at the receiving end.
For example, an arrayed waveguide grating (AWG) circuit, which is a conventional wavelength multiplexing/demultiplexing circuit, separates components of a multiplexed optical wave in the following manner:
That is, a wavelength multiplexed optical wave is input to the arrayed waveguide grating circuit through its input port and is then caused to pass through a plurality of (say, m) waveguides arranged in an array, whereby the multiplexed optical wave is separated into n components (optical waves) each having a single wavelength. Each of the optical waves with a different wavelength is output from a corresponding respective one of n output ports. The AWG circuit thus arranged is allowed to multiplex optical waves of different wavelengths the number of which is usually 30 to 60.
Recently, demands for optical communications have been remarkable and it is therefore required to further increase the number of channels.
However, an attempt to increase the number of channels with the conventional wavelength multiplexing/demultiplexing system would require the development of a new wavelength multiplexing/demultiplexing circuit having more arrayed waveguides. The development and manufacture of such a wavelength multiplexing/demultiplexing circuit require sophisticated techniques, which will result in very costly devices. In addition, the use of the new wavelength multiplexing/demultiplexing circuit would force the exchange of existing facilities including peripheral equipment, increasing the economical burden on users.
On the other hand, an arrangement has been proposed which increases the number of channels through the use of a number of multiplexers/demultiplexers using dielectric interference filters (for instance, DWDM components brochure by JDS FITEL, Dense wavelength Division Multiplexers (DWDM) Modules brochure by OPLINK COMMUNICATIONS). This arrangement is upgraded up to 16 or 40 channels with an eight-channel multiplexers/demultiplexers as one unit. Each unit is constructed by connecting, in stages, three-port multiplexers/demultiplexers using dielectric interference filters (for instance, Optical Add Drop multiplexers (OADM) Modules brochure by OPLINK COMMUNICATIONS). In this arrangement, a three-port multiplexer/demultiplexer is used for each channel so that the succeeding channel suffers reflection loss from the preceding three-port multiplexer/demultiplexer cumulatively.
From this reason, each channel suffers more transmission loss than the preceding one, thus, in the multiplexing/demultiplexing unit, the transmission loss varies greatly from channel to channel use is, therefore, at most 8 or 16. Even in multichannel arrangement in which the units are connected in stages the maximum increased number of channels is limited to at most 40 or 64.